<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        .big{
            width: 300px;
            height: 300px;
            background: skyblue;
            position: absolute;
            
        }
        .smaill{
            width: 150px;
            height: 150px;
            background: blue;
            position: inherit
        }
        .img{
            background: url('./img/a.png') no-repeat;
            width: 100%;
            height: 100%;
            position: fixed;
            background-origin: content-box;
            
           /*  background-size: cover;
            background-clip: content-box;
            background-origin: content-box;
            overflow-y: scroll; */
        }
    </style>
</head>
<body>
    <!-- <div class="bigs">
        <div class="big">这是大正方形
            <div class="smaill">这是大正方形</div>
        </div>
    </div> -->
    <div class="img"></div>
</body>
</html>